tmp/tmptsb35rml/{from.md → to.md}
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#### Exposition-only entities, etc. <a id="expos.only.entity">[[expos.only.entity]]</a>
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Several entities and *typedef-name*s defined in [[support]] through
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[[thread]] and [[depr]] are only defined for the purpose of exposition.
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The declaration of such an entity or *typedef-name* is followed by a
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comment ending in *exposition only*.
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The following are defined for exposition only to aid in the
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specification of the library:
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``` cpp
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namespace std {
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template<class T>
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requires convertible_to<T, decay_t<T>>
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constexpr decay_t<T> decay-copy(T&& v)
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noexcept(is_nothrow_convertible_v<T, decay_t<T>>) // exposition only
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{ return std::forward<T>(v); }
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constexpr auto synth-three-way =
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[]<class T, class U>(const T& t, const U& u)
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requires requires {
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{ t < u } -> boolean-testable;
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{ u < t } -> boolean-testable;
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}
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{
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if constexpr (three_way_comparable_with<T, U>) {
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return t <=> u;
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} else {
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if (t < u) return weak_ordering::less;
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if (u < t) return weak_ordering::greater;
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return weak_ordering::equivalent;
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}
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};
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template<class T, class U=T>
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using synth-three-way-result = decltype(synth-three-way(declval<T&>(), declval<U&>()));
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}
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```
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